This section introduces aspects that may help facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Also known as collaborative spatial multiplexing (CSM), multi-user multiple input multiple output (MU-MIMO) is a communication system feature that allows multiple users, each served by the same sector, to simultaneously transmit or receive on the same set of time-frequency resources. For some description of related developments, see, for example, 3rd Generation Partnership Project 2, “Overview for Ultra Mobile Broadband (UMB) Air Interface Specification,” 3GPP2 C.S0084-000-0, v2.0, August 2007; R. Bachl et al., “The Long Term Evolution Towards a New 3GPP* Air Interface Standard,” Bell Labs Tech. J., 11:4 (2007), 25-51; and Institute of Electrical and Electronics Engineers, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” IEEE 802.16-2004, June 2004, the disclosures of which are incorporated by reference herein in their entirety. By employing simultaneous transmissions and therefore increasing net spectral efficiency, MU-MIMO can allow the peak aggregate transmission rate to increase and may provide the potential to improve system performance (e.g. throughput, coverage).
While the above-cited standards may specify procedures that provide support for such a feature (e.g., overhead for feedback and signaling to indicate MU-MIMO transmissions), there are a number of challenges related to ranking transmissions to meet desirable system performance and on grouping MU-MIMO eligible transmissions.